Gujarat Board GSEB Textbook Solutions Class 12 Biology Chapter 16 Environmental Issues Textbook Questions and Answers, Additional Important Questions, Notes Pdf.
Gujarat Board Textbook Solutions Class 12 Biology Chapter 16 Environmental Issues
GSEB Class 12 Biology Environmental Issues Text Book Questions and Answers
What are the various constituents of domestic sewage? Discuss the effects of sewage discharge on a river.
Domestic sewage includes biodegradable pollutants such as animals and human excreta, dissolved organic compounds, nitrates and phosphates, sodium, potassium, calcium and chloride ions. Usually, these pollutants undergo rapid decomposition, but sometimes they accumulate in larger quantities in the field and cause problems.
The sewage may also percolate through the soil and reach the water table and contaminate the drinking water. Besides, the sewage kills the living fish and other aquatic animals and reduces the oxygen content of the water, and causes excessive growth of microorganisms (algal bloom) and aquatic vegetation. This process is known as eutrophication. Under such conditions, the oxygen content is very low and the river water becomes foul-smelling due to putrefaction and the river becomes degraded.
Due to the high growth of micro-organisms, the biological oxygen demand (BOD) of the water increases. BOD is a test of the amount of oxygen needed for bacteria to break down the organic matter in a water sample over a period of five days.
List all the wastes that you generate, at home, school or during your trips to other places, could you very easily reduce? Which would be difficult or rather impossible to reduce?
Food wastes, plastic bottles and covers, used cloths etc are the common wastes that we produce. Of these, plastic wastes can be reduced by other biodegradable materials.
Discuss the causes and effects of global warming. What measures need to be taken to control global warming?
Effects of Greenhouse Gases:
Global Temperature: The amount of carbondioxide is constantly rising by increasing deforestation, fossil fuel burning etc. Other gases like methane, chlorofluorocarbons, nitrous oxide etc. are also increasing since 18th century. Per capita carbondioxide emissions are highest for industrialized countries, and development of countries with high pollutions, such as China and India, can be expected to add large quanties of CO2 to the atmosphere in the near future. The amount of CO2 dissolved in oceans is about 60 times the amount of CO2 gas in the atmosphere. Increased levels of CO2 in the oceans lower the ocean water pH. This will strongly affect the organisms that live in ocean water.
The excessive increase in the amount of greenhouse gases in the atmosphere raises the temperature by retaining more infrared radiations. This excessive greenhouse effect is referred to as global warming.
Carbondioxide is the most important greenhouse gas that plays a major role in increasing global warming. 60% of the global warming is caused by carbondioxide. Chlorofluorocar-bon, nitrous oxide and methane constitute the remaining 40% of the global warming.
Drought is one of the most serious problems arising from major climatic change resulting from greenhouse warming or global warming. A three degree warming would be accompanied by 10% decrease in precipitation. Increased evaporation reduces water available for agricultural, municipal and industrial uses.
International concern over global warming led to a meeting of 160 nations in Kyoto, Japan, in December 1997. At that meeting, the U.S. proposed stabilizing emissions of greenhouse gases to 1990 levels during the period 2008-2012. But this meeting has met with severe criticism in the U.S. because the developing countries are expected to produce increasing fractions of greenhouse gases in the future. The global temperature trends are recorded since 1880 . 1980s were the w7armest ten year period recorded and the 1990s continued the trend. 2000 was the warmest year, as observed in the figure.
Sea Level Rise: The most damaging consequence of our pollution of the planet, as far as human civilization is concerned, is rise in sea level. Even if we manage to correct the imbalance of gases in the atmosphere, sea levels would go on rising for a long time. This is one of the potential surprises and shocks that the UN’s scientists face today.
The science about sea level rise is not simple. There are two main reasons for the rising of oceans. They are (1) thermal expansion of water and (2) melting of glaciers.
1. Thermal expansion of water: When the earth is heated up, the thermal expansion of water takes place. The 1995 estimate is that over the last 100 years the global sea level has risen by about 1-2.5mm in every year or 10-25cm in total. This is a slightly higher estimate than that made in 1990. The south-east of England is sinking due to rise of sea level.
Thermal expansion is one of the major causes of the sea level rise in the last century and it will be in the next also. Calculation is not quite easy because water expands at different amount at different temperature. Sir John Houghton calculated temperature variations in different areas of ocean. Thus sea level rise as a result of thermal expansion would be uneven across the globe.
2. The melting of glaciers: The second cause of sea level rise is the melting of glaciers such as those in the European Alps. All over Europe glaciers are said to have been in retreat since the middle of the last
century. It means, large amounts of glaciers or mass of ice once lying on mountain tops are moving to the oceans and making them deeper. The retreat of all glaciers in the last century has added 2 to 5cm (1-2 in) to sea level.
Many of the smaller glaciers are expected to disappear completely
Approaches to deal with global warming:
Mitigation of the perils of global warming involves taking actions aimed at stabilizing global atmospheric concentrations of greenhouse gases. They include
- Reducing the greenhouse gas emissions by limiting the use of fossil fuels, switching to renewable sources of energy (e.g. hydrogen fuel cells, wind energy, solar energy, nuclear power, tidal and ocean energy, geothermal power, etc.), and by the use of fossil fuels that produce the least of greenhouse gases such as CNG (compressed natural gas).
- Adoption of energy conservation methods that include increasing the fuel efficiency of vehicles.
- Carbon capture and storage (CCS) is a plan to mitigate climate change by capturing carbon dioxide (CO2) from large point sources such as power plants and subsequently storing it away safely instead of releasing it into the atmosphere.
- Carbon sequestration is another approach that involves the removal of carbon from the atmosphere. A variety of means of artificially capturing and storing carbon are being explored.
- Increasing the vegetation cover, particularly the forests, for photosynthetic utilisation of CO2
- Minimizing the use of nitrogen fertilisers in agriculture for reducing N,0 emissions.
- Developing substitutes for chlorofluorocarbons. For example, replacing the CFCs with hydrochlorofluorocarbons (HCFCs) or hydrofluorocarbons (HFCs).
in the next century. Icebergs are carried to the oceans by glaciers. Glaciers of the Alps are the best documented, but the glaciers are disappearing in Alaska and Washington state. If all the glaciers were to disappear completely as the world warms up, the sea would rise by as much as 50cm (nearly 20 in).
Due to global warming, the polar ice sheets undergo melting and this will directly influence the sea level rise. In this situation, many cities and coastal areas will disappear from the earth. The rising of sea level produces negative impacts on human existence, freshwater resources, agricultural and drylands, animals and birds existence etc.
The current estimates for sea level rise are for IS cm (S in) by 2030, and about 50 cm (20 in) by the end of the twenty-first century.
Match the items given in columns A and B:
|a. Catalytic converter
|i. Particulate matter
|b. Electrostatic precipitator
|ii. Carbon monoxide and nitrogen oxides
|iii. High noise level
|iv. Solid wastes
a. ii b. i c. iii d. iv
Write critical notes on the following:
b. Biological magnification
c. Groundwater depletion and ways for its replenishment
a. Domestic sewage and fertilizers add large quantities of nutrients such as nitrates and phosphates to the freshwater ecosystem. The rich supply of these nutrients makes blue-green algae, green algae, and other planktons grow abundantly. This increased productivity of water bodies brought about by nutrient enrichment is known as eutrophication.
b. Some chemicals used in biocides are not degradable or degraded very slowly in nature. The long-range effects of such chemicals are in fact a threat to our ecological security. Indiscriminate use of such chemicals could make them an integral part of our biological, geological, and chemical cycles of the earth. Once they are absorbed by an organism, they cannot be metabolized or excreted out. These pollutants get deposited in fat-containing tissues.
For instance, if a non-degradable pollutant DDT enters a pond, it is taken as such by the plants, then reaches to zooplankton, then to fishes and finally in the body of birds who eat the fish. A more threatening factor is that the DDT concentration continuously increases in successive trophic levels in a food chain. This phenomenon is called biological amplification of biological magnification.
c. Due to overpopulation and urbanisation the level of groundwater is decreasing. This depletion can be replenished by harvesting rainwater, protecting natural water bodies, sustainable use of water, etc.
Why ozone hole form over Antarctica? How will enhanced ultraviolet radiation affect us?
Ozone is a denser form of oxygen that shields the Earth from excessive ultraviolet radiation from the sun; without it, the earth’s inhabitants and environment are exposed to damaging UV-B rays. Scientists detected substantial seasonal fluctuations in stratospheric ozone levels over Antarctica as early as the 1950s. In the 1970s the chemists Sherwood Rowland and Mario Molina of the University of California (in findings later confirmed by the National Academy of Sciences) blamed the lower wintertime level of ozone over Antarctica on the rapidly increasing use of chlorofluorocarbons (CFCs) as refrigerants and as propellants in aerosol cans and in the manufacture of plastic foam products.
CFC molecules deplete the ozone layer because they migrate to the stratosphere, collect over the Antarctic ice cap during the cold winter months, and become fixed on polar stratospheric clouds, isolated from the normal atmospheric circulation.
When sunlight returns to Antarctica in early spring, its ultraviolet rays trigger a chemical reaction that releases a chlorine-oxide-free radical, which precipitates another reaction that breaks up the oxygen molecules that form the ozone layer.
A world that has been producing and releasing into the atmosphere 1 million tons of CFCs per year has seen CFC levels in the atmosphere rise from 0.8 parts per billion by volume in 1950 to at least 4 parts per billion at the close of the century. The CFC gases act as catalysts and also due to the action of UV rays, the amount of concentration of ozone gets thinned, leading to the formation of the ozone hole.
Due to the depletion of ozone layer the dangerous UV-B radiation passes through this layer and reaches the earth. The incidence of UV-B radiation
- causes skin cancer, cataract and other severe diseases to man.
- diminishes the function of immune system.
- affects photosynthesis
- causes the production of increased amounts of ozone in the atmosphere, which cause’ photochemical smog.
Discuss the role of women and communities in the protection and conservation of forests.
(i) Bishnois – are group of followers of Guru Janbeshwar Maharaj, a small community inhabiting a village near Jodhpur in Rajasthan. They are known for peaceful co-existence with nature. In 1731, once when king of Jodhpur, asked his fellow people to arrange wood for new palace, they reached Bishnois village. Effort of cutting trees was thwarted by Bishnois. A Bishnois women Amrita Devi hugged the trees and daring King’s men to cut her before cutting the trees. But, kings men cut the tree down along with her. Her 3 daughters and 100 other Bishnois followed her and all lost their lives saving trees. Now there is Amrita Devi Bishnoi Wildlife Protection Award given to individuals or communities from rural area who show courage and dedication to protect wildlife and trees.
(ii) Chipko movement – of Garhwal Himalayas. In 1974, local women showed extreme courage by hugging trees and protecting them from the axe of contractors.
(iii) Appiko movement – Conservation, plantation and Rational use is their belief.
(iv) Joint Forest Management (JFM) – The government of India in 1980s introduced the concept of JFM so as to work closely with local communities for protecting and managing forests. In return for their service, they were rewarded with various benefits and forest were conserved in. sustainable manner. Communities got benefit of various forest products like fruits, gum, rubber, medicine etc.
What measures, as an individual, you would take to reduce environmental pollution?
- Encourage afforestation
- Prevent deforestation
- Controlled tapping of groundwater.
- Reduction of the production and use of plastic, sprayer etc.
- Use of solar energy in place of petroleum gases.
- Protect our ponds and water bodies.
Discuss briefly the following:
a. Radioactive wastes
b. Defunct ships and e-wastes
c. Municipal solid wastes
Radioactive wastes – Nuclear energy
(source of non-polluting electricity) has 2 important problems
- Accidental leakage (Chernobyl incident);
- safe disposal is a problem for radioactive waste.
Radiations are extremely damaging to organisms, because of its mutations at very high rate. At high doses, it is lethal but at lower doses, creates various disorders like cancer, anomaly, etc. Their disposal is also a serious issue. Low level and intermediate level wastes do not produce – heat and other environmental problems, so are safe dumping in process inside proper containers. But high-level wastes which release lots of heat and cause environmental problems are put in suitable containers and buried 500 m deep inside rocks inside the earth.
(b) Defunct ships and e-wastes. Defunct ships – old ships are dismantled to obtain scrap and other useful materials mainly in developing countries, due to less labour charge and low tax. Workers engage in ship breaking are exposed to a number of toxicants like asbestos, lead, mercury etc. The coastal area associated with a ship-breaking yard in also polluted.
e-wastes (electronic wastes) – They are increasing due to the increased use of e-equipments and rapidly changing technologies. From it metals (copper, iron, silicon, nickel, gold) etc. are extracted. Dismantling also exposes them to toxic substances.
(c) Municipal solid wastes – Domestic waste office wastes, school, public sweeping, sludge from sewage treatment plants, vegetables, fruit markets. They may be bio-degradable or non-bio-degradable. They consist of paper (40%), food waste (7%), glass, crockery, rubber,- leather, plastics etc. Their disposal is mainly done by Pig and cattle feeding, salvage, Burning, incineration, landfills, pyrolysis (heat), composting, Biogas plants, Recycling etc.
What initiatives were taken for reducing vehicular air pollution in Delhi? Has air quality improved in Delhi?
Delhi leads the country in its levels of air pollution with its large vehicular traffic. In the 1990s, Delhi ranked fourth among the 41 most polluted cities in the world.
Delhi’s registered vehicular population has nearly doubled to 4.5 million from 2.2 million in 1994, registering a growth rate of 10% per annum. About two-thirds of the motor vehicles are two-wheelers.
Vehicular pollution is considered to be a major source of air pollution in Delhi. As per Central Pollution Control Board, the vehicular pollution load in Delhi increased by nearly 50% in 1995-96 from 1990-91. However, a decrease has been witnessed in recent years with the implementation of several control measures. Vehicular emission load reported by the Central Pollution Control Board is under:
Steps Taken by Delhi Govt, to reduce the Pollution in Delhi :
Pollution Checking by Transport Department: Mobile enforcement teams are being deployed on regular basis at road locations for the prosecution of polluting vehicles and vehicles not having Pollution Under Control (PUC) Certificates.
Public Awareness: Public awareness campaigns are conducted to raise social consciousness on the issue and educate motorists about the health hazards, statutory pro-visions and control measures viz. engine tuning and maintenance.
Since April 1995, only those 4-wheeled petrol-driven vehicles are registered on the first sale in Delhi, which is fitted with Catalytic Converters.
Mass Rapid Transport System: Mass Rapid Transport System is being constructed with the objective to place a non-polluting, efficient, and affordable rail-based mass rapid transport system for NOT of Delhi, duly integrated with other modes of transport.
Phasing out of Old Commercial Vehicles: With a view’ to reduce vehicular pollution in Delhi Honhle Supreme Court vide its orders in CWP No. 13029 of 1985 has banned the plying of following categories of vehicles in Delhi:
More than 15 years old commercial/ transport vehicles, Autos & Taxis driven on conventional fuels and diesel driven city buses
Transport Department is ensuring the effective compliance of these directions through its enforcement teams. The Govt, of Delhi, has provided fiscal incentives by way of sales tax exemption and interest subsidy on loans for the purchase of new replacement vehicles. All the buses of Delhi were converted to run on compressed natural gas (CNG).
Tightening of mass emission standards for new vehicles: Mass emission norms for new vehicles were introduced in the year 1991. Subsequently, these norms have been tightened for new vehicles in all categories in 1996 and 2000. At present, only vehicles (except 2 and 3 wheelers) complying with Bharat Stage III/Euro-III emission norms, and 2 and 3 wheelers complying with Bharat Stage II/Euro-II emission norms are being registered in Delhi.
Improvement in Fuel Quality: The quality of the fuel being supplied in Delhi has been significantly improved during recent years.
Discuss briefly the following:
a. Greenhouse gases b. Catalytic converter c. Ultraviolet B
a. Due to overpopulation and deforestation, industrial and domestic coal-burning releases a high amount of carbon dioxide into the environment. The amount of carbon monoxide emitted by automobiles, other gases like chlorofluorocarbons (CFCs), methane (CH4), nitrous oxide (N2O) etc. increase in the atmosphere. These gases have the ability to absorb infrared radiation. These gases are known as greenhouse gases. They form an envelope around the earth and prevent the re-radiation from the earth. So these radiations are again reflected back to earth.
b. A reaction chamber typically containing a finely divided platinum-iridium catalyst into which exhaust gases from an automotive engine are passed together with excess air so that carbon monoxide and hydrocarbon pollutants are oxidized to carbon dioxide and water.
c. Of or relating to the range of invisible radiation wavelengths from about 4 nanometers, on the border of the x-ray region, to about 380 nanometers, just beyond the violet in the visible spectrum.
GSEB Class 12 Biology Environmental Issues Additional Important Questions and Answers
Name any 3 gases contributing to greenhouse effect. (CBSE 2004)
CO2, methane (CH4), Nitrous oxide (N2O).
Name an instrument used in vehicles to reduce air pollution.
What are ODS. Give examples. (CBSE 2005)
Certain substances react with ozone present in the stratosphere and destroy the ozone. They are called ozone-depleting substances or ODS. The majors ODS are CFCs, halons (gases used in fire extinguisher i. e. like bromo chloride fluoro methane), N2O, CH4, Cl etc.
Name the Act passed by the Government of India to protect and improve the quality of our environment.
Environment (Protection) Act, 1986
India will have Euro III emission norm complaint automobiles and fuels by the year
What is the name given to irreparable computers and other electronic goods?
Electronic waste (e-waste)
Inflammation of cornea due to high dose of UV-B radiation is called
Motor vehicles equipped with catalytic converter should use only unleaded petrol. Justify.
Lead in the petrol inactivates the catalyst.
Many villagers near Industrial are sufferers from “blue baby syndrome! How is this problem caused? (CBSE 2004)
From the industries, nitrate-containing impurities add to the water causes water pollution. When these people drink this water, nitrite changes into nitrate and passes into blood and oxidises ferrous of haemoglobin to ferric ion. This way formed hemoglobin is called methemoglobin. This reduces, the oxygen-carrying capacity of blood. This results in cyanosis in infants called blue baby syndrome.
We have got used to associating loud sounds with pleasure and entertainment not realising that noise causes psychological and physiological disorders in humans. Comment on the various ill effects of noise in human.
- Brief exposure to extremely high sound level 150 dB or more may 111 damage eardrums. r-7:
- Chronic exposure to a relatively lower noise level of cities may c permanently damage the hearing ability of humans.
- Noise also causes sleeplessness, increased heart beating, altered breathing patterns and stress.
Briefly explain the different measures to reduce noise pollution.
- Reduction of noise from industries by using sound absorbent materials or by muffling noise.
- Delimitation of horn-free zones around hospitals and schools.
- Limit the use of loudspeakers especially from 9 pm – 9 am.
- Use of crackers within permissible sound levels.
CNG is better than other conventionally used fossil fuels. Comment.
- CNG burns most efficiently and very little of it is left unburnt.
- CNG is cheaper than petrol or diesel.
- It cannot be siphoned off by thieves.
- It cannot be adulterated like petrol or diesel.
What is meant by algal bloom?
The excessive growth of certain phytoplankton, facilitated by the excess presence of nutrients in the water bodies is called algal bloom.
Write a short note on algal bloom.
Presence of large amounts of nutrients in water causes excessive growth of planktonic algae. This phenomenon called as algal bloom which imparts a distinct colour to the water bodies. Algal blooms cause deterioration of the water quality and fish mortality. Some bloom-forming algae are extremely toxic to human beings and animals.
Sewage treatment can be done by integrating artificial and natural processes. Explain this using the example of Areata town.
The people of Areata with biologists created an integrated wastewater treatment process within a natural system. The cleaning occurs in two stages.
a. The conventional sedimentation, filtering, and chlorine treatments are given. The remaining pollutants were removed in the second stage.
b. The biologists developed a series of six connected marshes over 60 hectare of marshland. Appropriate plants algae, fungi and bacteria were seeded into this area which neutralise, absorb and assimilate the pollutants. Hence as the water flows through the marshes, it gets purified naturally.
Are sanitary landfills a practical solution to dispose solid waste? Why?
No. Landfills are not really much of a solution since the amount of garbage generation specially in the metros has increased so much that these sites are getting filled too. Also there is danger of seepage of chemicals from these landfills polluting the underground water resources.
Enumerate some important measures for controlling global warming.
- Cutting down use of fossil fuel.
- Improving the efficiency of energy usage.
- Reducing deforestation.
- Planting trees.
- Slowing down the growth of the human population.
Global warming is due to the greenhouse effect. Explain both the greenhouse effect and global warming.
The greenhouse effect is the phenomenon of warming of the earth due to the greenhouse gases like CO2, CH4, NO2, CFC, etc. The increase in the global mean temperature is called global warming.
“Eutrophication can lead to the death of a lake” Discuss.
- The main pollutants in sewage, industrial wastes, and agricultural runoff are nitrates and phosphorus.
- These pollutants stimulate the growth of algae which leads to the depletion of oxygen in water bodies, causes the death of aquatic organisms.
- Other toxic substances flowing into the lake can kill all the fishes and other animals in the water.
- Due to the decomposition of these bodies the oxygen level further decreases in the water body
- Ultimately this leads to the death of the lake.
You have been appointed as the minister for food, agriculture, and the environment. Write down 6 laws you would like to implement in order to save our environment (write in the order of priority).
- Encourage afforestation
- Prevent deforestation
- Controlled tapping of groundwater.
- Reduction of the production and use of plastic, sprayer, etc.
- Use of solar energy in place of petroleum gases.
- Protect our ponds and water bodies.
What would be the impact on the environment around a thermal power plant if its electrostatic precipitator stops functioning? Give a reason.
An electrostatic precipitator can remove 99% of particulate matter present in the exhaust from a thermal power plant. So if it. stops functioning, it causes breathing and respiratory problems, irritation, inflammation and damage to the lungs, and premature deaths.
The figure given below shows the relative contributions of various greenhouse gases to total global warming.
i. Name the gases (a) and (b).
ii. Explain how an increase in greenhouse gases in the earth’s atmosphere leads to the melting of ice caps.
i. a. N2O
b. Methane (CH4)
ii. The rise in temperature is leading to deleterious changes in the environment and results in climatic changes. Thus leading to increased melting of polar ice caps as well as of other places like the Himalayan snowcaps.
Microbes play a dual role when used for sewage treatment as they not only help to retrieve usable water but also generate fuel. ‘Write how this happens?
Sewage is treated in sewage treatment plants to make it less polluting. This treatment is carried out in two stages.
- Primary treatment: Primary treatment is a physical process of removal of small and large particles through filtration and sedimentation.
- Secondary treatment: It is a biological process, that employs the heterotrophic bacteria naturally present in the sewage.
- The bacterial flows are allowed to sediment, which is called activated sludge. The remaining major part of the sludge is pumped into large tanks called anaerobic sludge digesters.
During this digestion, bacteria produce a mixture of gases.
Here these gases form biogas and can be used as a source of energy as inflammable.
The above diagram shows a simplified biogeochemical cycle.
i. Name the compound whose cycle is depicted.
ii. In what way do vehicles add this compound to the atmosphere?
iii. What adverse effect does its excess have on the environment?
iv. Cite an event that depicts this effect in modern times.
v. Suggest two ways of reducing this effect.
i. The compound is carbon and this cycle is called the carbon cycle.
ii. The vehicles produce poisonous gases which add to the atmosphere and pollute it. This is very harmful to respiratory organs like the lungs.
iii. If the carbon gases exceed in air, living things face many problems like respiration because the total quantity of global carbon is 71% in the atmosphere.
iv. Human activities have significantly influenced the carbon cycle. Rapid deforestation and massive burning of fossil fuel for energy and transport have significantly increased the rate of release of carbon dioxide into the atmosphere which causes greenhouse effects.
v. Stop deforestation
Reduce the massive burning of fossil fuels.
Create an aquatic food chain in a water body into which effluents flow from a pesticide factory. Diagrammatically represent biomagnification in this food chain.
A few toxic substances often present in industrial wastewaters, can undergo biological magnification in the aquatic food chain. An increase in the concentration of the toxicant at successive trophic levels refers to biomagnification. This is due to a toxic substance accumulated by an organism that cannot be metabolised or excreted and thus, passes on to the next higher trophic level. This phenomenon is well known for mercury and DDT.
The figure shows the biomagnification of DDT in an aquatic food chain. In this manner, the concentration of DDT is increased at successive trophic levels. If it starts at 0.003 ppb (part per billion) in water, it can ultimately reach 25 ppm (parts per million) in fish-eating birds, through biomagnification. The high concentration of DDT disturbs calcium metabolism in birds, which causes thickening of eggshell and their premature breaking eventually causing a decline in bird populations.
What is the greenhouse effect? Discuss the effect of increased levels (between 540 and 970ppm.) of carbon dioxide gas on the growth of C3 plants.
As a result of the increase in greenhouse gases like CO, CFCs, CH4, N2O etc., the environmental temperature increases at the surface level. This process is called the greenhouse effect. CO2 is the most abundant greenhouse gas in the atmosphere. An increase in the level of CO2 leads to CO2 fertilization which causes an increase in the growth of C3 plants by 30%.
What is meant by ozone hole? When does it develop every year? How are CFCs responsible for this?
The ozone hole is the thinning of the ozone layer in the stratosphere and it is marked over the Antarctica region. It develops every year in late August and early October.
In the stratosphere, the VU rays act on the CFCs and release chlorine atoms. These chlorine atoms degrade the ozone layer by acting as a catalyst. Since the chlorine atom is not consumed in the reaction the CFCs have a permanent and continuing effect on ozone holes.
Study the graph given below and answer the questions that follow.
i. What is the relationship between dissolved oxygen and biochemical oxygen demand (BOD)?
ii. Mention their effect on aquatic life in the river.
i. BOD refers to the amount of the oxygen that would be consumed if all the organic matter in one liter of water were oxidized by bacteria.
ii. Microorganisms involved in the biodegradation of organic matter in the water body consume a lot of oxygen, and as a result, there is a sharp decline in dissolved oxygen downstream from the point of sewage discharge. This causes the mortality of fish and other aquatic creatures.